Variable length boom and selfleveling platform therefor



June 29, 1954 F. J. SCHMIDT VARIABLE LENGTH BOOM AND SELF-LEVELING PLATFORM THEREFOR Filed May 31 1950 vmzm giz L 3 I Patented June 29, 1954 VARIABLE LENGTH BOOM AND SELF- LEVELING PLATFORM THEREFOR Fred Joseph Schmidt, Fort Wayne, Ind., assignor to American Steel Dredge Company, Inc., Fort Wayne, Ind., a corporation of Indiana Application May 31, 1950, Serial No. 165,178

4 Claims. 1

The present invention relates to booms, and more particularly to an extensible boom carrying a platform and including automatically operating mechanism to maintain the platform in a horizontal plane while the boom is being raised or lowered and while it is being extended or retracted.

One object of the invention is to provide a new and improved boom including means for varying the end-to-end length thereof.

Another object of the invention is to provide a new and improved boom comprising body sections relatively movable telescopically to increase or decrease the end-to-end length of the boom.

A further object of the invention is to provide a new and improved means for automatically maintaining a platform or cage carried upon a boom in a level plane while it is being raised and lowered by the boom.

A still further object of the invention is to provide a new and improved means for restraining tilting of a platform, cage, or the like, rockably carried upon a boom, when the loads on opposite sides of the pivot axis of the platform are unequal.

A more general object of the invention is to provide a new and improved extensible boom which is inexpensively constructed but nevertheless extremely sturdy and simple to expand and retract.

Another object of the invention is to provide a new and improved means for maintaining a platform carried on a boom in a horizontal plane, the means being simple and inexpensive in construction, reliable in operation, not subject to breakdown, and adaptable for use on booms of fixed or variable length.

These and other objects, advantages and capabilities of the invention will become apparent from the following description, wherein reference is had to the accompanying drawings, in which:

Fig. 1 is a side elevational view of the improved boom of the present invention, showing the same at one elevation in full lines and at a lowerelevation in phantom;

Fig. 2 is a top plan view of the boom disclosed in Fig. 1;

Fig. 3 is an enlarged detail top plan View of the lower end of the boom; and

Fig. 4 is an enlarged detail top plan view of the upper end of the lower boom section together with a portion of the upper boom section.

Referring to Fig. 1, it will be seen that the boom of the present invention comprises a nonsection I2 longitudinally extensible relative to the nonextensible section Ill. The lower boom section I!) may be fabricated from angle iron members of appropriate sizes and may be of more or less conventional open truss-work construction. It may have a plurality of longitudinal chords l4 rectangularly arranged and interconnected by truss members including diagonally extending side members I6 connecting the upper and lower longitudinal chords M (Fig. 1) on each side of the boom and crossed truss members l8 interconnecting the two upper chords M to each other, as seen in Fig, 2. Like cross members interconnect the two lower chords l4.

Adjacent its lower or fixed end the nonextensible lower boom section [0 is also reinforced by reinforcing plates 29 and by additional crosspieces, one of which is shown at 22 (Fig. 2)

The lower end of the nonextensible section H! has a pair of generally triangular brackets 24 anchored on the respective sides of the section It (Figs. 1 and 3). Shaft 26 (Figs. 2 and 3), passing through the brackets 24, is supported in generally triangular pedestals or brackets 28 fixed to a platform shown more or less diagrammatically at 30. The platform 30 may be any suitable stationary platform or it may be a rotatable platform of standard construction carried by any suitable prime mover in the usual manner. In any event the winches or drums and other operating mechanism necessary to operate the boom, along with the source of power for operating the same, will normally be located on a portion of this platform 30 beyond that which is shown. Since these various parts may be of standardized construction and are available on the market, a detailed description thereof is thought to be unnecessary.

Shaft 26 forms an axis upon which the boom may be rocked in a vertical plane and for this purpose a cable 32 is provided wound around a sheave 34 rockable in a clevis or yoke 36 which is pivotable upon a shaft 38 carried at the free end of the nonextensible boom section In. The shaft 38 is supported adjacent opposite ends in upwardly extending angle members 40 on the outer end of the nonextensible boom section Ill reinforced by bracing 42. The end of the cable 32 extending through the sheave 34 is anchored to itself, thus to form a loop reeved on the sheave 34. At its opposite end this cable is reeled upon a suitable reel or winch (not shown) which may be power operated to raise and lower the boom in a vertical plane in the usual manner.

The extensible section 12 of the boom preferably comprises a pair of longitudinally extending channel members 44 having webs or sides 48 and flanges 48. These channel members are disposed in spaced relation, with their flanges 48 extending inwardly toward each other, by reinforcing truss structure including a plurality of crossed members 50 (Fig. 2) and cross plates 52. The ends of the crossed members 58 and cross plates 52 are secured to the inwardly facing sides of the flanges 48 on the channel members 44.

These channel members should be of less height than the external height of the nonextensible section ID of the boom, as seen in Fig. 1, and should be spaced from each other a distance appreciably less than the external width of the nonextensible section, as seen in Fig, 2, so that the extensible section I2 may be readily be received in the nonextensible section Ill.

The extensible section [2 is supported in the nonextensible section in for relative extensible and retractable movement by a series of opposed pairs of upper and lower guide rollers, the upper guide rollers being shown at 54 in Fig. 2 and the lower rollers being similar to these upper rollers. These rollers are fixed upon shafts 56 and are spaced sufficiently from each other so that radially extending flanges 58 on the rollers will loosely engage the opposite sides 46 of the extensible boom section I2.

The roller shafts 56 are rotatably supported adjacent their opposite ends in brackets 68 fixed transversely to the opposed upper and lower chords I4 of the nonextensible boom section I0, the upper and lower shafts 58 in each opposed pair of shafts being spaced sufliciently so that the peripheries of the rollers 54 on these shafts loosely engage, respectively, the upper and lower flanges 48 on the channels 44 of the extensible boom section I2. These shafts 56 are suitably fixed against endwise movement to maintain the extensible boom section I2 centered relative to the nonextensible section II).

The extensible boom section I2 is extended and retracted relative to the nonextensible section Ill by a pair of cables including a cable 82 for extending the extensible section I2, and a cable 64 for retracting this section. Cable 62 is suitably anchored at one end to an intermediate part of the extensible boom section I2 and passes over a sheave 66 rotatably supported adjacent the upper end of the nonextensible boom section III. At its other end this cable is wound on a power operated winch or reel (not shown).

The other cable 64 is suitably anchored at one end to the lower end of the extensible boom section I2 and passes over one of two duplicate sheaves 68 rotatably carried adjacent the lower end of the lower boom section and to a power operated winch or reel (not shown).

Thus by providing winches or reels of like size for the two cables 62 and 64, and by operating these winches at uniform speed but in opposite directions, the extensible boom section I2 may be extended or retracted while the boom as an entirety may be rocked about the axis of the boom shaft 26 by means of the cable 32.

Retraction of the extensible section I2 is limited by a stop adjacent the pivot end of the nonextensible section It] comprising vertically extending members I fixed at opposite ends to the previously mentioned transverse angle members 22 near the fixed end of the nonextensible boom section II].

An extensible boom for various purposes is thus provided. In actual practice, not more than one-third to one-half of the length of the extensible boom section should be extended beyond the nonextensible section so that the length of the coextensive portions of the two boom sections will be of sufiicient extent rigidly to support the extensible section I2 in the nonextensible section I0.

In the drawing the boom is shown carrying a cage I2 on its outer end, of the type in which workmen may be supported while they are engaged in performing operations at elevated positions relative to the ground level. This cage I2 has side walls I4 and a platform or floor I8. One of the features of the present invention is the novel means which has been provided for maintaining the floor of this cage in a horizontal plane while the boom is being rocked to raise or lower the cage 12 and while the extensible section I2 is being extended or retracted.

Referring to Fig. 2, it will be seen that a yoke I8 is fixed to the outer end of the extensible boom section l2. The cage I2 is suspended from the yoke by means of heavy pins 88 carried by the opposite arms of the yoke I8 and engaged with the opposite sides of the cage I2 to form a pivot axis for the cage at a point intermediate the horizontal length of the cage.

Spaced a short distance from the yoke I8 an arm 82 is rockably carried upon a horizontal axis by the extensible boom section I2. A crank 84 fixedly secured relative to the rockable arm 82 is connected to the cage I2- by a link 86. It will be apparent, therefore, that as the rockable arm 82 is rocked on its connection with the boom, the cage I2 will be rocked on its pivotal connection with the yoke I8 on the boom, and that by rocking the rockable arm 82 in correlated relation with the raising or lowering of the cage I2 by the boom, the floor I6 of the cage may be maintained in a horizontal plane during such movement of the boom.

The novel means for so moving the rockable arm 82 includes an arm 88 (Fig. 1) fixedly secured to the platform 30 adjacent one of the pedestals 28 by means of a pair of bars 90 and 92 which support the arm at a predetermined angle to the vertical. Upper and lower tension cables 94 are fixed at their lower ends to the opposite ends of the fixed arm 88. These cables 94 are reeved over sheaves 9B rotatably mounted on opposite sides of the axis of rockable arm 82 adjacent the opposite ends of this arm, and over sheaves 98 rotatably carried on stud shafts 99 on the opposite sides 46 of the extensible boom section I2 (Figs. 1 and 4) spaced outwardly from its lower end and anchored at their other ends to the upper end of the lower section II) of the boom, as indicated at I00 (Fig. 1).

Since the opposite ends of the tension cables 94 are dead-ended, respectively, on the fixed arm 88 and the upper end of the lower boom section l0, while corresponding bights in these cables pass over the sheaves 96 carried on opposite ends of rockable arm 82, any increase in tension in one cable 94 over that in the other will cause a force to be applied on the sheave 96, over which the more highly tensioned cable is reeved and the end of the rockable arm 82 to which that sheave is secured, greater than that applied to the other end of the rockable arm. As a result, the rockable arm 82 will rock sufiiciently to equalize the tension in the two cables 94 and will rock the cage I2 through the crank arm 84 and link 86.

Thus by initially adjusting tension in the cables 94 while the boom is at a particular elevation to cause the cage 12 to assume a position at which its floor is horizontal, the cage will thereafter he maintained at a position at which its floor is horizontal while the boom is raised or lowered. This results from the fact that movement of the boom, raising or lowering the outer end thereof, varies the distance between the opposite ends of the fixed arm 88 and the corresponding ends of rockable arm 82 along the opposite tensioned cables 54, thus varying the tension in these two cables and causing the rockable arm 82 to be rocked sufiiciently to equalize the tension in these cables. Suitable proportioning of the relative lengths of the fixed arm 88, the rocker 82 and the crank 84 insures smooth and reliable operation.

When the extensible boom section H1 is extended or retracted, the sheaves at on rockable arm 82 move in the same direction and the same distance as the sheaves 98 on channels M. Under the circumstances no change in the tension in the upper or lower cables 9 1 occurs and, therefore, the cage 12 is not rocked on its pivotal connection with the yoke 18. Its floor, therefore, remains in the same plane.

Preferably the tension in the cables 94 is so adjusted initially and the connection between the rockable arm 82 and cage 72 is such that the rockable arm '82 is always maintained parallel to the fixed arm 88 when the boom is raised and lowered, as indicated in full and phantom lines in Fig. 1. Initial adjustment of the tension in the cable 94 may be made in any suitable manner and any adjustment thereafter made necessary by wear or expansion may be made by means of turnbuckles H12 in each of the cables 94.

From the foregoing description of the construction of the improved mechanism of the present invention, its operation will be apparent and, therefore, will not be repeated. However, it is to be noted that in addition to operating to maintain the fioor of cage It horizontal while it is being raised or lowered by the boom, the leveling apparatus of the present invention also operates to restrain tilting of the cage 12 on its pivot axis 80, should the loads on opposite sides of this axis be unequal.

Since the boom and the apparatus for maintaining the floor of cage 12 horizontal may be made from standard parts, the invention is capable of being inexpensively constructed, yet functions entirely satisfactorily. Furthermore, the leveling means is reliable in operation both in maintaining the floor of cage T2 in a horizontal plane when the boom is being raised and lowered, and also in preventing tilting of the cage at all times.

While I have shown and described a preferred embodiment of my invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. I, therefore, desire, by the following claims, to include within the scope of the invention all such Variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. A boom structure comprising a support, a first boom section pivotally connected at one end to the support for swinging movement in a vertical plane, a second boom section movable telescopically with respect to the first boom section, a platform rockably carried adjacent the outer end of the second boom section, a fixed member on the support, a rocker pivotally mounted on the second boom section upon a generally horizontal axis, means forming an operative connection between the rocker and the platform for rocking the latter when the rocker is rocked, and means to rock the rocker in correlation with swinging movement of the boom sections including a pair of sheaves pivotally'secured to the rocker respectively on opposite sides of its rocking axis, a second pair of sheaves rotatably mounted respectively on the second boom section between the rocker and the inner end of the second section, and a pair of tension cables of fixed length reeved over the respective sheaves on the rocker and over the respective sheaves of the second pair and dead-ended on the fixed member and on the first boom section adjacent its outer end, so that swinging movement of the boom in a vertical plane, sufiicient to vary the distance along the cable from the sheaves to the fixed member, generates variations in the tension in the cables sufiicient to rock the rocker in order to tilt the platform to maintain the latter horizontal.

2. A boom structure comprising a support, a first boom section pivotally connected at one end to the support for swinging movement in a vertical plane, a second boom section movable telescopically with respect to the first boom section, a fixed member on the support, a rocker pivotally mounted on the second boom section for tilting movement in a generally vertical plane, and means to rock the rocker in correlation with swinging movement of the boom sections including a pair of sheaves pivotally secured to the rocker respectively on opposite sides of its rocking axis, a second pair of sheaves rotatably mounted respectively to the second boom section between the rocker and the inner end of the second section, and a pair of tension cables of fixed length reeved over the respective sheaves on the rocker and over the respective sheaves of the second pair and dead-ended on the fixed member and on the first boom section adjacent its outer end, so that swinging movement of the boom in a vertical plane, sufiicient to vary the distance along the cables from the sheaves to the fixed member, generates variations in the tension in the cables sufficient to rock the rocker in order to maintain the latter in a predetermined angular relationship with the support.

3. A boom structure comprising a support, a first boom section pivotally connected at one end to the support for swinging movement in a vertical plane, a second boom section movable longitudinally with respect to the first boom section to vary the length of the boom, a rocker pivotally mounted on the second boom section for rocking movement in a generally vertical plane, and means to rock the rocker in correlation with swinging movement of the boom sections in a vertical plane and to prevent rocking of the rocker due to relative longitudinal movement of the sections, including a pair of sheaves pivotally secured to the rocker respectively on opposite sides of its rocking axis, a second pair of sheaves rotatably mounted individually on the second boom section between the rocker and the inner end of the second section, and a pair of tension cables of fixed length reeved over the respective sheaves on the rocker and over the respective sheaves of the second pair and deadended on the support and on the first boom section adjacent its outer end, so that swinging movement of the boom suflicient to vary the distance along the cables from the sheaves to the fixed member generates variations in the tension in the cables suflicient to rock the rocker in order to maintain the latter in a predetermined angular relationship with the support.

4. In a device of the class described, a support, a boom pivotally connected at one of its ends to said support for swinging movement in a vertical plane, a cage rockably carried adjacent the other end of said boom, a fixed member on said support, a vertically disposed rocker on said boom spaced from said cage, a link pivotally secured at one end to said rocker and at the other end to said cage, said points of pivotal securement being respectively spaced from the center of rotation of said rocker and said cage approximately equally and in parallel directions, and means to rock said rocker in correlated relation with swinging movement of the boom in a vertical plane including a pair of sheaves pivotally secured to said rocker respectively on opposite sides of its rocking axis, and a pair of tension cables of fixed length reeved over the respective sheaves on said rocker and dead-ended on said fixed member and an intermediate part of said boom so that swinging movement of the boom in a vertical plane suflicient to vary the distance along said cables from the opposite sheaves to said fixed member generates variations in the tension in the two cables suflicient to rock said rocker the amount necessary to rock the cage for maintaining its floor horizontal.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,418,775 Brown June 6, 19 22 1,506,277 Strauss Aug. 26, 1924 2,331,558 McEwen et al Oct. 12, 1943 2,362,170 Swaisgood Nov. 7, 1944 2,457,049 Lacey Dec. 21, 1948 2,500,815 Gerli et al Mar. 14, 1950 FOREIGN PATENTS Number Country Date Great Britain 1898 

